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Slideshow: Valentine's Day in the Animal Kingdom

Humans aren't the only species to form lasting bonds with our mates—nor are we the only ones to step out, break up, or move on when circumstances change. But hey, at least we don't eat our partners during sex. From "till death do us part" to "till someone better comes along," here are a few of the many forms of monogamy in the animal kingdom.

Credit: Glenn Grant, National Science Foundation

Emperor Penguins

Emperor penguins (Aptenodytes forsteri) are famous for their familial devotion, with males incubating a single egg for more than 2 months while their mates travel to the sea for food. But their commitment typically lasts for only one breeding season. Emperor penguins usually latch onto a mate quickly after returning to the colony, and if the previous year’s partner isn’t around, he or she will find someone else.

Credit: DickClarkMises, Made Available Under the Creative Commons CC0 1.0 Universal Public Domain Dedication

Black Vultures

If you want a true avian symbol of till-death-do-us-part monogamy, look no further than the black vulture (Coragyps atratus). They may feed on abandoned carcasses, but they never step out on their lifelong partners. Plus, these symbols of death share 24-hour babysitting duty.

About one-third of red-backed salamanders (Plethodon cinereus) pair up each summer, rare behavior among amphibians. Bonded males get a bit peevish if their partner visits another potential mate, nipping her or performing threatening displays. Cuckolded females, however, have been known to body slam their fickle partners.

Credit: Thinkstock

Seahorses

Scientists have studied only a handful of species of seahorses (genus Hippocampus), but all of them appear to practice some form of monogamy. After her eggs are fertilized, a female seahorse passes them to her male partner, who carries them in a pouch until they hatch. The males probably incubate one female’s eggs at a time, and it appears that some species remain bonded throughout the breeding season and perhaps even longer.

These South American monkeys (genus Callicebus) hate being separated from their mates, and often kiss, nuzzle, and even hold hands while they’re together. While the emotional bond lasts until one partner dies, they do often turn to other monkeys for sex.

Credit: Thinkstock

Gray Wolves

Packs of wolves (Canis lupus) usually include a dominant breeding pair, along with several generations of kids and the occasional aunt or uncle. While breeding pairs usually remain bonded until one partner dies and were long considered truly monogamous, a study in Yellowstone National Park revealed that some males were mating with several females and causing rivalries within the pack.

Credit: Thinkstock

Beavers

Beaver parents and children (genus Castor) live together in the homes they build and usually remain devoted partners for their whole lives. But some research suggests that when extra mates start hanging around, even these family-oriented homebodies become more promiscuous.*

Credit: Sturgis McKeever, Georgia Southern University, Bugwood.org

Brown Widow Spiders

Monogamy is forced on the male brown widow spider (Latrodectus geometricus), as the first female he mates with concludes their time together by snacking on his abdomen. Luckily, the cannibalism seems to prolong the sex, thereby promoting the doomed male’s reproductive success.

*Clarification 14 February: This item has been updated with a correct picture of beavers.